Integrated circuits typically comprise a number of layers formed on a silicon substrate. As integrated circuits become smaller, and the thickness of layers comprising the integrated circuits is reduced, the behavior of devices formed from these layers often depends on the thickness or composition of a specific layer. For example, a transistor formed on a silicon substrate may have different characteristics depending on the thickness or composition of the gate of the transistor. It may therefore be useful to determine a thickness and composition of a layer in a microelectronic device such as an integrated circuit.
The thickness or composition of a layer in a microelectronic device such as an integrated circuit may be determined using one of several techniques. The microelectronic device typically includes a structure including several layers built up over a substrate. Techniques that may be used to determine a thickness and/or composition of a specific layer in a structure include ellipsometry, using an electron probe with wavelength dispersive spectrometer(s), angle-resolved x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectrometry (SIMS).
Angle-resolved XPS uses photoelectron spectroscopy to determine a thickness and/or composition of a layer or multiple layers. Photoelectron spectroscopy bombards a sample with photons having a specific wavelength (here, x-ray photons), which excite the atoms of the sample to generate a photoelectron having a characteristic energy for the sample. The technique depends on measuring photoelectrons at different emission angles from the sample surface, for example by tilting the sample with respect to an electron energy analyzer.
As technologies advance, improved methods for determining thickness and compositions of thin layers are needed.